[BLDG-SIM] Condensing Boiler Curve HIR

[Jeremy Cockroft]

Brandon,
 
We just implemented, in ESP-r, an upgraded boiler model that accepts a
series of coefficients to represent a complex curve fit involving both
return water temperature and firing rate, which are the key parameters
determining condensing boiler efficiency.  The coefficents for the model
equation are generated using an Excel spreadsheet calculator, with data
input exactly like what is in the graph in your ELCCA post.  In our
modelling scheme we allow for outdoor air compensation acting directly
on the boiler flow temperature setpoint (aquastat setting) both for
on-off and modulating versions of the boiler model.  Other than that, it
is just our two node boiler model for the dynamic part.  More info on
this is contained in a project report at
http://www.sesg.strath.ac.uk/Downloads/Report_BRE_E302_040707.pdf (look
at P6).
 
Hope this is of interest.

Jeremy Cockroft

Energy Systems Research Unit
University of Strathclyde
75 Montrose Street
Glasgow G1 1XJ
phone    +44(0)141 548 5765
fax         +44(0)141 552 5105
email       jeremy at esru.strath.ac.uk
website   www.esru.strath.ac.uk <http://www.esru.strath.ac.uk/> 

________________________________

From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Brandon
Nichols
Sent: 10 August 2007 20:12
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Condensing Boiler Curve HIR



All,
 
Some time ago I began developing this post
<http://elcca-exchange.blogspot.com/2006/12/equest-boiler-curve-example.
html>  describing the derivation of a condensing boiler HIR performance
curve based on boiler supply and return water temperature.
 
By popular request and the requirements of a current project, I now have
the incentive to actually try implementing it.  
 
This has turned out to be not as simple as I would've expected, when
using the HIR-FT performance curve in the parametric run, there is no
change from the baseline case with a constant 1.25 HIR.  A couple of
things I noticed that might be contributing to the problem:
 
* While the built-in performance curve HIR-FT function implies on the
eQuest dialog box that it is a function of boiler EWT and LWT, the
DOCUMENTATION states that the lesser parameter is supplied by either the
zone temperature or the outdoor temperature, depending on the value of
the LOCATION keyword.  Is HIR-FT a function of boiler return water
temperature (i.e. EWT) or not?
 
* It is impossible to set via the dialog box the HIR-FPLR to 'undefined'
in the baseline case; when 'undefined' is selected,
'Atmospheric-Blr-HIR-fPLR' jumps back as the default on leaving the
dialogue.  Could this performance curve be overriding the the HIR-FT
performance curve?
 
* While it should be trivial for someone more familiar with BDL to
simply define a keyword expression (or input macro or function... hmm,
which one?) to compute the HIR based on EWT and LWT, however I do not
know which approach to take (expression, macro, or function) and could
not find a reference in the DOE2.2 documentation for accessing
dynamically changing parameters, specifically either the boiler or
circulation loop supply and return temperatures.
 
* Lastly, I have specified the loop supply temperature to vary based on
an OSA reset schedule, but in the case of the condensing boiler I would
also like the boiler aquastat setpoint to be reset (this presumably will
reset the temperature of the boiler LWT).  A similar problem to the HIR
function, but perhaps simpler would be to make the aquastat setpoint
track exactly with the loop supply temp, which is being reset as
expected.  How can AQUASTAT-SETPT-T be set to equal the dynamically
changing value of the circulation loop setpoint? 
 
 
Thanks in advance...
 
 
Brandon Nichols, PE
Mechanical
HARGIS ENGINEERS

600 Stewart Street

Suite 1000

Seattle, WA 98101

www.hargis.biz

 

d | 206.436.0400  c | 206.228.8707

o | 206.448.3376  f  | 206.448.4450

 
 

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